U.S. patent application number 12/096941 was filed with the patent office on 2009-09-10 for electrostatic spray apparatus and method of electrostatic spray.
Invention is credited to Mitsuhiro Fukuoka, Mitsuhiro Takahashi.
Application Number | 20090224437 12/096941 |
Document ID | / |
Family ID | 38162696 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090224437 |
Kind Code |
A1 |
Fukuoka; Mitsuhiro ; et
al. |
September 10, 2009 |
ELECTROSTATIC SPRAY APPARATUS AND METHOD OF ELECTROSTATIC SPRAY
Abstract
An electrostatic spray apparatus configured such that multiple
spinning units, each having multiple nozzles arranged
two-dimensionally to electrostatically spray a polymer solution and
a first collector disposed so as to be opposed to the multiple
nozzles via an insulating sheet, are installed on collecting
sections for holding a moving collecting sheet, and such that an
air stream is formed orthogonal to the spray direction from the
nozzles to the first collector and toward the collecting sheet
inside the spinning unit.
Inventors: |
Fukuoka; Mitsuhiro; (Ehime,
JP) ; Takahashi; Mitsuhiro; (Ehime, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK L.L.P.
1030 15th Street, N.W., Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
38162696 |
Appl. No.: |
12/096941 |
Filed: |
September 27, 2006 |
PCT Filed: |
September 27, 2006 |
PCT NO: |
PCT/JP2006/319111 |
371 Date: |
June 11, 2008 |
Current U.S.
Class: |
264/465 ;
425/174.8E |
Current CPC
Class: |
D04H 1/42 20130101; D04H
1/56 20130101; Y02P 70/62 20151101; D01D 5/0061 20130101; D01F
13/00 20130101; Y02P 70/625 20151101 |
Class at
Publication: |
264/465 ;
425/174.8E |
International
Class: |
D01D 5/04 20060101
D01D005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2005 |
JP |
2005-357401 |
Claims
1. An electrostatic spray apparatus comprising: multiple spinning
units each having multiple nozzles arranged two-dimensionally to
electrostatically spray a polymer solution containing a polymeric
substance and formed into a liquid using a solvent and a first
collector disposed so as to be opposed to said multiple nozzles via
an insulating sheet, the polarity of the voltage applied to said
first collector being different from that of the voltage applied to
said nozzles or said first collector being grounded to the ground
potential, a first power supply for applying a predetermined high
voltage to said nozzles, and a collecting section provided with
said spinning units and movably holding a collecting sheet, wherein
said spinning unit is provided with air stream forming means
flowing in a direction substantially orthogonal to the spray
direction from said nozzles to said first collector for forming an
air stream toward said collecting sheet.
2. The electrostatic spray apparatus according to claim 1, wherein
said air stream forming means has an air intake port formed at a
position opposed to the installation face of said spinning unit
that is installed on said collecting section, and a conductive
member to which a power supply having the same polarity as that of
the voltage applied to said nozzles is connected is provided at
said air intake port, second collectors having conductivity are
disposed behind said collecting sheet in said collecting sections,
and the polarity of the voltage applied to said second collector is
different from that of the voltage applied to the conductive member
at said air intake port or said second collector is grounded to the
ground potential, and said collecting sheet is fed along the faces
of said second collectors.
3. The electrostatic spray apparatus according to claim 1, wherein
said spinning unit has a conductive plate made of a conductive
metal and integrally molded with said nozzles, said polymer
solution is stored in the concave section formed in said conductive
plate, and said polymer solution is supplied to said nozzles.
4. The electrostatic spray apparatus according to claim 1, wherein
said spinning unit comprises: said first collector disposed so as
to be opposed to said nozzles, said insulating sheet disposed
between said nozzles and said first collector, and said air intake
port formed on the face opposed to said installation face installed
on said collecting section to generate an air stream toward said
collecting section in a direction substantially orthogonal to the
spray direction of said polymeric substance.
5. The electrostatic spray apparatus according to claim 1, further
comprising: a feed roller around which said collecting sheet is
wound in a roll state, and a take-up roller for taking up said
collecting sheet that is fed from said feed roller and moved inside
said collecting section and on which said polymeric substance is
laminated.
6. The electrostatic spray apparatus according to claim 2, wherein
said multiple spinning units are each installed on said collecting
section having said collecting sheet disposed in a direction
substantially orthogonal to the direction of said air stream, and
said second collector of said collecting section attracts said
polymeric substance electrostatically sprayed so that said
polymeric substance is laminated on said collecting sheet thereby
to form a polymeric web.
7. The electrostatic spray apparatus according to claim 1, wherein
the pressure inside said collecting sections is set to a negative
pressure that is lower than the ambient air pressure.
8. The electrostatic spray apparatus according to claim 1, wherein
said collecting sections are each provided with a recovery unit
into which the air inside said spinning units flows to recover the
solvent contained in said polymer solution.
9. The electrostatic spray apparatus according to claim 1, wherein
said multiple spinning units are disposed continuously in the
movement direction of said collecting sheet.
10. The electrostatic spray apparatus according to claim 1, wherein
the height of said nozzle is 5 mm or more, and the inside diameter
of the spray port at the tip of said nozzle is in the range of 0.1
to 1.0 mm.
11. The electrostatic spray apparatus according to claim 1, wherein
said spinning units installed on said collecting sections are
configured so as to be removable.
12. A method of electrostatic spray comprising the steps of:
feeding a polymer solution containing a polymeric substance and
formed into a liquid using a solvent to multiple nozzles arranged
two-dimensionally, applying a high voltage to said nozzles to
electrostatically spray said polymer solution from said nozzles,
generating an air stream flowing in a direction substantially
orthogonal to the direction of electrostatic spray in each of
spinning units having said nozzles, and applying said air stream to
said polymeric substance electrostatically sprayed and charged so
that said polymeric substance is laminated on a collecting sheet
disposed substantially orthogonal to the direction of said air
stream.
13. The method of electrostatic spray according to claim 12, having
the step of laminating said polymeric substance on said collecting
sheet by moving said polymeric substance electrostatically sprayed
and charged in a direction orthogonal to the spray direction from
said nozzles by the Coulomb forces.
14. The method of electrostatic spray according to claim 12, having
the operation of always detecting the holding amount of said
polymer solution and maintaining the level of said polymer solution
constant in the step of supplying said polymer solution containing
said polymeric substance and formed into a liquid using a solvent
to said multiple nozzles.
15. The method of electrostatic spray according to claim 12,
wherein the polarity of the voltage applied to said first collector
disposed so as to be opposed to said nozzles is different from that
of the voltage applied to said nozzles or said first collector is
grounded to the ground potential to generate attraction forces to
attract charged liquid droplets separated from said nozzles,
electrostatically sprayed and formed into minute charged
particles.
16. The method of electrostatic spray according to claim 12,
wherein the polarity of the voltage applied to said second
collector disposed along the side of said collecting sheet opposite
to the side on which said polymeric substance is laminated is
different from that of the voltage applied to said nozzles or said
second collector is grounded to the ground potential to generate
attraction forces to attract minute charged particles
electrostatically sprayed from said nozzles.
17. The method of electrostatic spray according to claim 12, having
the step of recovering said solvent contained in said polymer
solution from said air streams in said spinning units.
18. The method of electrostatic spray according to claim 12, having
the step of laminating said polymeric substance on the same
collecting sheet by independently operating said multiple spinning
units having said nozzles.
19. The method of electrostatic spray according to claim 18, having
the step of controlling the operation states of said multiple
spinning units depending on the specifications of a polymeric web
to be produced.
20. The method of electrostatic spray according to claim 18, having
the step of laminating a different polymeric substance on said
collecting sheet in at least one of said multiple spinning units.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrostatic spray
apparatus and a method of electrostatic spray for electrostatically
spraying a solution containing a polymeric substance.
BACKGROUND ART
[0002] Electrostatic spray (electrospinning) is carried out
according to the following procedure in which a polymeric substance
serving as a material desired to be used for coating is mixed with
a solvent to make a solution, the solution is stored in a container
having a pointed tip, such as the needle tip of a syringe or a thin
glass pipe, and a high voltage is applied between the container and
an object to which the polymeric substance is sprayed. In the
electrostatic spray, charges are provided to the polymeric
substance inside the container, the charged polymeric substance is
emitted in an atomized form due to the repulsion forces acting
between the charges from the tip of the container to the side
referred to as a collector having a polarity different from that of
the spray side (the tip side of the container) or to the ground
side using the Coulomb forces and then collected and laminated on
the collector side. Electrostatic coating is a technique in which
electrostatic spray is used, and it is generally known that
electrostatic coating is applied to vehicle bodies, such as
automobile bodies. Electrostatic coating is not limited to vehicle
body coating, but is applicable to the coating of various types of
products. The present invention relates to an apparatus
particularly adapted for electrostatically spraying an artificial
polymeric substance as a material and more particularly relates to
an apparatus capable of easily producing nonwoven fabrics formed of
fibers thinner than 100 nanometers [nm] in diameter, referred to as
nanofibers. Nonwoven fabrics produced in this way can be used in a
wide range of applications including filters.
[0003] Filters can also be produced for example using the "fusion
method" that is one of methods for producing conventional nonwoven
fabrics. However, filters formed of fibers several ten micrometers
in diameter are mainly produced using such a conventional
production method, and filters formed of fibers of several hundred
nanometers are the limit of the products that can be produced using
the conventional method. On the other hand, the production method
using electrostatic spray can produce nonwoven fabrics formed of
fibers thinner than those in the case of the conventional
production method such as the "fusion method" by one or two orders
of magnitude as described above. When only one nozzle having a
spray port is used for electrostatic spray, only small filters of
several centimeter square can be produced. Hence, the configuration
wherein only one nozzle having a spray port is used is not
realistic in view of mass productivity and productivity. When
filters having a width of 100 cm or an equivalent size are produced
by textile manufacturers and original fabric manufacturers, it is
necessary to use multiple nozzles as in the cases of nonwoven
fabrics and films having been produced using the conventional
production method.
[0004] However, when multiple nozzles are used, there is a problem
that the operation state of electrostatic spray becomes unstable
due to the effects of interference, repulsion, etc. of charges, and
some or most of the multiple nozzles disposed cannot carry out
electrostatic spray in some cases. Hence, carrying out stable
electrostatic spray using multiple nozzles is a task that must be
achieved to put an electrostatic spray apparatus having multiple
nozzles into practical use and to mass-produce products.
[0005] To achieve the above-mentioned task, a mechanism for
suppressing the interference and repulsion of charges, referred to
as a charge distribution plate, has been proposed in Japanese
Patent Application Laid-Open Publication No. 2002-201559. However,
the charge distribution plate is difficult to handle since the
position of the charge distribution plate must be changed depending
on the voltage applied to carry out electrostatic spray.
Furthermore, in the case that multiple nozzles are arranged in row
and column directions, there is a problem that the ratio of the
coating amount (lamination amount) to the spraying amount, the
so-called collection efficiency, becomes lower when the charge
distribution plate is used.
[0006] Furthermore, a system in which electrodes are disposed on
the nozzles and the mounting face of an object to which a material
is sprayed and a high voltage is applied therebetween has been
disclosed in Japanese Patent Application Laid-Open Publication No.
H 8-153669. In the system in which the electrodes are disposed on
the nozzles and the installation face and electrostatic spray is
carried out for the object to which a material is sprayed as
described above, the electrostatically sprayed material is
laminated so as to cover the mounting face, that is, the surface of
the opposed electrode, and the capability of the electrostatic
spray becomes weak gradually. Hence, in the production method
disclosed in Japanese Patent Application Laid-Open Publication No.
H 8-153669, it is difficult to carry out electrostatic spray with
high accuracy for a long time, and the method is not suited for
mass production.
[0007] Patent document 1: Japanese Patent Application Laid-Open
Publication No. 2002-201559
[0008] Patent document 2: Japanese Patent Application Laid-Open
Publication No. H 8-153669
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0009] Material particles having been charged and electrostatically
sprayed are attracted to a collector serving as a collecting face
(lamination face) having charges of a different polarity and then
collected (laminated) on the collector. Since the material
particles sprayed have the same polarity, they are repulsed from
one another due to the Coulomb forces and dispersed, and then reach
the collector in a uniform state. At the same time when the
material particles are collected (laminated) on the collector, the
charges thereon are discharged to the collector. Even after the
charges are discharged, the collector is required to hold the
amount of charges equivalent to the amount of charges on the
material particles at all times, the polarity of the charges being
different from that of the charges on the material particles, or
the collector is required to be grounded. The reason why is that
when the sprayed material particles are attracted and collected
continuously on the collector, in the case that the collector holds
the amount of charges equivalent to the amount of charges on the
material particles, the polarity of the charges being different
from that of the charges on the material particles, or the
collector is grounded, no charges are accumulated between the spray
ports of the nozzles and the collector. As a result, the material
particles are smoothly attracted from the spray ports to the
collecting face (lamination face), and electrostatic spray is
carried out. However, as the amount of charges on the sprayed
material particles increases, charges are accumulated between the
spray ports and the collector. Since the polarity of the charges
accumulated as described above is the same as that of the charges
on the material particles to be sprayed, the charges are repulsed
from one another according to Coulomb's law and suppressed from
being sprayed from the spray ports, resulting in a phenomenon in
which electrostatic spray cannot be carried out from the spray
ports of the nozzles. This kind of phenomenon occurs similarly in a
configuration in which one nozzle is disposed and in a
configuration in which multiple nozzles are disposed. The inventors
of the present invention conducted experiments using electrostatic
spray apparatuses having a configuration in which one nozzle is
disposed and a configuration in which multiple nozzles are
disposed, and the inventors have found a phenomenon that
electrostatic spray is stopped when the amount of charges on the
polymeric material is increased by gradually raising the applied
voltage. However, since the amount of charges on the polymeric
material to be sprayed in the electrostatic spray apparatus having
one nozzle is smaller than that in the electrostatic spray
apparatus having multiple nozzles, it is easier to carry out
electrostatic spray in the configuration of the electrostatic spray
apparatus having one nozzle.
[0010] When multiple nozzles are used to raise productivity, the
amount of charges increases inevitably, the charges are repulsed
intensely from one another, and electrostatic spray is thus
prevented from being carried out in many cases. Hence, it is
necessary to reduce the amount of charges, more specifically, to
lower the voltage to be applied. However, if the voltage to be
applied is lowered in this way, there occurs a problem that the
spray speed drops and the productivity lowers. Furthermore, the
repulsion forces between the charges are required for spray from
the spray ports at the tips of the nozzles. If the amount of
charges is reduced by lowering the voltage to be applied, the
repulsion forces required for spray become insufficient, and spray
cannot be carried out in some cases.
[0011] Hence, when electrostatic spray is carried out in the
configuration provided with multiple nozzles under the same
conditions, for example, the same voltage and same spray distance,
as those in which electrostatic spray can be carried out
efficiently in the configuration provided with one nozzle, some or
most of the multiple nozzles cannot carry out electrostatic spray
in many cases. Therefore, to carry out electrostatic spray, the
electrostatic spray apparatus provided with multiple nozzles is
required to have a special configuration under the conditions in
which electrostatic spray can be carried out efficiently in the
configuration provided with one nozzle.
[0012] For example, in a conventional electrostatic spray
apparatus, the collector is disposed in parallel with the spray
ports of the multiple nozzles, the collector is made of a highly
conductive material, such as aluminum foil, so that charges are not
accumulated between the spray ports and the collector, and/or the
area of the collector is made as large as possible. However, even
in this kind of configuration, the effect is limited to some extent
and not improved dramatically. Hence, the configuration does not
provide a fundamental solution.
[0013] Furthermore, the conventional electrostatic spray apparatus
is low in collection efficiency even when electrostatic spray is
carried out and causes a problem that collection (lamination) at
only the intended locations cannot be carried out and particles not
collected are dispersed around the apparatus. The inventors have
found this kind of problem of dispersion by carrying out
electrostatic spray using the apparatus covered with an acrylic
cover or the like. This kind of problem that the sprayed material
particles cannot be collected (laminated) causes a loss of the
material as a matter of course. In addition, since the large amount
of fibers of several nanometers to several ten nanometers in
diameter is dispersed, attention must be given to the health
hazards of workers.
[0014] Accordingly, the present invention is intended to provide an
electrostatic spray apparatus and a method of electrostatic spray
capable of carrying out electrostatic spray stably using multiple
spray means and capable of mass-producing products at high
collection efficiency, excellent productivity, high accuracy and
high safety.
Means for Solving Problems
[0015] The electrostatic spray apparatus and the method of
electrostatic spray according to the present invention are
configured as described below to solve various problems encountered
in the above-mentioned conventional electrostatic spray
apparatuses.
[0016] The electrostatic spray apparatus according to the present
invention comprises:
[0017] multiple spinning units each having multiple nozzles
arranged two-dimensionally to electrostatically spray a polymer
solution containing a polymeric substance and formed into a liquid
using a solvent and a first collector disposed so as to be opposed
to the multiple nozzles via an insulating sheet, the polarity of
the voltage applied to the first collector being different from
that of the voltage applied to the nozzles or the first collector
being grounded to the ground potential,
[0018] a first power supply for applying a predetermined high
voltage to the nozzles, and
[0019] collecting sections provided with the spinning units and
movably holding a collecting sheet, wherein
[0020] the spinning unit is provided with air stream forming means
flowing in a direction substantially orthogonal to the spray
direction from said nozzles to said first collector for forming an
air stream toward the collecting sheet. The electrostatic spray
apparatus according to the present invention configured as
described above can carry out electrostatic spray stably and
continuously at high collection efficiency.
[0021] The method of electrostatic spray according to the present
invention comprises the steps of:
[0022] feeding a polymer solution containing a polymeric substance
and formed into a liquid using a solvent to multiple nozzles
arranged two-dimensionally,
[0023] applying a high voltage to the nozzles to electrostatically
spray the polymer solution from the nozzles,
[0024] generating an air stream flowing in a direction
substantially orthogonal to the direction of electrostatic spray in
a spinning unit having the nozzles, and
[0025] applying the air stream to the polymeric substance
electrostatically sprayed and charged so that the polymeric
substance is laminated on a collecting sheet disposed substantially
orthogonal to the direction of the air stream. The above-mentioned
method of electrostatic spray according to the present invention
can securely carry out electrostatic spray stably at high
collection efficiency.
EFFECT OF THE INVENTION
[0026] The present invention can provide an electrostatic spray
apparatus and a method of electrostatic spray capable of
mass-producing products at high collection efficiency, excellent
productivity and high accuracy using multiple nozzles arranged
two-dimensionally and serving as spray means.
[0027] Furthermore, since an organic solvent evaporating during the
electrostatic spraying process can be recovered securely, the
present invention can provide an electrostatic spray apparatus and
a method of electrostatic spray having high safety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a view showing the schematic configuration of an
electrostatic spray apparatus according to Embodiment 1 of the
present invention;
[0029] FIG. 2 is a schematic sectional view showing multiple
spinning units installed on the ducts of the electrostatic spray
apparatus according to Embodiment 1;
[0030] FIG. 3 is a perspective view showing the spinning unit of
the electrostatic spray apparatus according to Embodiment 1;
[0031] FIG. 4 is a view showing the installation face of the
spinning unit of the electrostatic spray apparatus according to
Embodiment 1;
[0032] FIG. 5 is a view showing the rear face of the spinning unit
of the electrostatic spray apparatus according to Embodiment 1;
[0033] FIG. 6 is a sectional view showing a spray block and its
surrounding area in the spinning unit of the electrostatic spray
apparatus according to Embodiment 1; and
[0034] FIG. 7 is an exploded perspective view showing the spray
block and its surrounding area in the spinning unit of the
electrostatic spray apparatus according to Embodiment 1.
EXPLANATION OF NUMERALS
[0035] 1 nozzle [0036] 2 conductive plate [0037] 3 charged
particles [0038] 4 first collector [0039] 5 insulating sheet [0040]
6 air intake port [0041] 7 second collector [0042] 8 collecting
sheet [0043] 9 insulating cover [0044] 10 housing [0045] 11 flange
[0046] 12 installation hole [0047] 13 collecting section [0048] 14
material supply pipe [0049] 15 material holding tank [0050] 16
metal net [0051] 17 air stream [0052] 18 intermediate roller [0053]
19 recovery unit [0054] 20 feed roller [0055] 21 take-up roller
[0056] 22 spinning unit [0057] 30 spray block [0058] 40 first power
supply [0059] 50 second power supply
BEST MODES FOR CARRYING OUT THE INVENTION
[0060] A preferable embodiment of an electrostatic spray apparatus
and a method of electrostatic spray according to the present
invention will be described below in detail referring to the
accompanying drawings.
Embodiment 1
[0061] FIG. 1 is a side view showing the schematic configuration of
an electrostatic spray apparatus according to Preferred Embodiment
1 of the present invention. The electrostatic spray apparatus
according to Embodiment 1 sprays a solution containing a polymeric
substance from nozzles by electrostatic spray to fabricate fibers
thinner than 100 nanometers [nm], referred to as nanofibers, and to
produce nanofiber nonwoven fabrics.
[0062] First, the outline of the fabrication of nanofiber nonwoven
fabrics by the electrostatic spray of the electrostatic spray
apparatus according to Embodiment 1 of the present invention will
be described below referring to FIG. 1. A substrate serving as a
base is required to produce nanofiber nonwoven fabrics by
collecting and laminating nanofibers. A collecting sheet 8 formed
of an insulating resin sheet made of polyethylene for example is
used as the substrate. This collecting sheet 8 is fed from a feed
roller 20 and taken up by a take-up roller 21 via multiple
intermediate rollers 18, the transfer speed of which can be
controlled. The electrostatic spray apparatus according to
Embodiment 1 is configured such that the transfer speed of the
collecting sheet 8 is determined depending on the thickness of a
nonwoven fabric, the diameter and material of nanofibers, etc. and
so as to be able to meet a wide range of transfer speed from
several meters to several hundred meters per minute.
[0063] The collecting sheet 8 serving as a substrate is transferred
in the zone ranging from the feed roller 20 to the take-up roller
21 via the multiple intermediate rollers 18. Multiple spinning
units 22 are disposed along the transfer path of the collecting
sheet 8. The spinning units 22 are installed on the ducts of
collecting sections 13 incorporating the collecting sheet 8 on
which nanofibers are collected and laminated. As the collecting
sheet 8 passes through the inside of the collecting sections 13,
the nanofibers from the spinning units 22 are laminated on the
collecting sheet 8 to a thickness of several hundred nanometers to
several hundred micrometers.
[0064] As shown in FIG. 1, the spinning units 22 are installed in a
nearly horizontal direction on the side faces of the ducts of the
collecting sections 13 extending in the vertical or horizontal
direction so as to be orthogonal to the side faces, and are
configured so as to be independent of one another. The number of
the spinning units 22 to be installed is arbitrarily set depending
on the production speed, specifications, etc. of a nanofiber fabric
to be produced. The electrostatic spray apparatus according to
Embodiment 1 is configured such that the number of the spinning
units 22 to be installed can be arbitrarily selected from one to
the maximum number of the spinning units 22 installable on the
collecting sections 13. Furthermore, since the spinning units 22
are configured so as to be able to operate independently of one
another, only arbitrarily selected spinning units 22 can be
operated while all the spinning units 22 are installed. For this
reason, in the electrostatic spray apparatus according to
Embodiment 1, specific spinning units 22 can be removed for repair
or maintenance without stopping production. In addition, if an
accident occurs suddenly in some spinning units 22 during
production, the production can be continued by stopping only the
spinning units 22 relevant to the accident, without stopping the
entire apparatus.
[0065] Furthermore, in the electrostatic spray apparatus according
to Embodiment 1, materials to be supplied to the spinning units 22
are not required to be the same. Since the spinning units 22 are
each provided with a material holding tank 15 (see FIG. 2),
described later, for supplying a material to the nozzles, it is
possible to supply different kinds of materials to the respective
spinning unit 22 and to produce nonwoven fabrics formed of the
different kinds of materials laminated. It is also possible to
supply the same material to the respective spinning unit 22 and to
hold the same material in the respective material holding tank 15,
and it is further possible to supply the same material to the
respective spinning unit 22 at all times by connecting a common
supply pipe to the respective spinning unit 22, as a matter of
course.
[0066] Next, the configuration and operation of the spinning units
22 in the electrostatic spray apparatus according to Embodiment 1
will be described below.
[0067] FIG. 2 is a side sectional view showing the configuration of
the multiple spinning units 22 installed on the collecting section
13. FIGS. 3 to 5 are views showing the configuration of the
spinning unit 22; FIG. 3 is a perspective view showing the spinning
unit 22, FIG. 4 is a front view showing the front face serving as
the installation face of the spinning unit 22, and FIG. 5 is a rear
view showing the rear face of the spinning unit 22.
[0068] As shown in FIG. 2, each spinning unit 22 is provided with
the material holding tank 15 for storing a solution containing a
polymeric substance, and the solution is supplied from the material
holding tank 15 to multiple nozzles 1 provided inside the spinning
unit 22 via a material supply pipe 14. The multiple nozzles 1 are
integrally molded with a conductive plate 2 made of a conductive
material and serving as a metal block, and arranged
two-dimensionally and linearly in row and column directions (in a
lattice-like pattern). In the electrostatic spray apparatus
according to Embodiment 1, the conductive plate 2 has a function of
a solution reservoir for temporarily reserving the solution
containing the polymeric substance that is used as the material,
and the multiple nozzles 1 are disposed on the lower side of the
solution reservoir. The multiple nozzles 1 and the conductive plate
2 described above constitute a spray block 30 that is used as a
spray section.
[0069] A solution prepared by mixing a polymeric substance, such as
polyurethane, serving as the material of nanofibers with a solvent,
such as toluene, is supplied from each of the material holding
tanks 15 independently disposed on the respective spinning unit 22
to the conductive plate 2 of the spray block 30 configured as
described above via the material supply pipe 14.
[0070] In the electrostatic spray apparatus according to Embodiment
1, although the spray block 30 having the multiple nozzles 1 and
the conductive plate 2 is integrally molded from a metal block made
of a material, such as aluminum or stainless steel, by press
working, it may be made by cutting. The nozzle 1 has a spray port
of a predetermined diameter and is formed into a conical shape so
as to be pointed at the tip. In addition, the nozzle 1 is
configured such that its spray port communicates with the solution
reservoir of the conductive plate 2.
[0071] The conductive plate 2 is configured such that a high
voltage (for example, a high voltage between several kV to several
ten kV) is applied thereto from a first power supply 40, and the
upper portion thereof on which the nozzles 1 are not disposed is
covered with an insulating cover 9 made of an insulating resin.
With this insulating cover 9, the solution inside the solution
reservoir of the conductive plate 2 is kept in a state of being
prevented from being contaminated with dust, etc. Furthermore, in
the spinning unit 22, the spray block 30 is secured in a state of
being insulated from the housing 10 of the spinning unit 22 using
the insulating cover 9.
[0072] Furthermore, on the entire lower face of the inside of the
spinning unit 22, an insulating sheet 5 and a first collector 4
formed of a thin metal plate are stacked from above in this order
so as to be opposed to the nozzles 1. In the electrostatic spray
apparatus according to Embodiment 1, although the first collector 4
is grounded, it may be configured such that a voltage having a
polarity different from that of the spray block 30 is applied
thereto.
[0073] FIG. 6 is a sectional view showing the spray section of the
spinning unit 22 of the electrostatic spray apparatus according to
Embodiment 1, the spray section comprising the spray block 30, the
insulating cover 9 for covering the spray block 30, etc. In
addition to the spray block 30 and the insulating cover 9, the
material supply pipe 14 and the material holding tank 15 are
provided in the spray section. FIG. 7 is an exploded perspective
view of the spray section shown in FIG. 6.
[0074] The conductive plate 2 integrally molded with the multiple
nozzles 1 is formed into a tray shape. In the bottom face section
thereof, the multiple nozzles 1 each provided with a spray port
having a conical shape and pointed at the tip are arranged
two-dimensionally and linearly in row and column directions; in
other words, the multiple nozzles 1 are disposed at the
intersection positions of the lattice-like pattern at equal
intervals with one another. The spray block 30 having the
conductive plate 2 and the multiple nozzles 1 is integrally molded
from a metal block by press working as described above. The
solution containing the polymeric substance is stored in the space
of the tray section, that is, the concave space in the conductive
plate 2, and the solution is supplied from the material holding
tank 15 to the tray section via the material supply pipe 14 such
that the amount of the solution inside the tray section is
maintained constant. The multiple nozzles 1 disposed on the bottom
face of the conductive plate 2 are arranged at equal intervals in
the row and column directions. In Embodiment 1, 48 nozzles 1 are
formed in 4 rows and 12 columns on the conductive plate 2 measuring
250 mm (width).times.500 mm (length).times.180 mm (height). The
size of the conductive plate 2 and the number of the nozzles 1
described above are merely examples and set appropriately depending
on the specifications, production speed, etc. of a fabric to be
produced, the voltage applied to the nozzles 1 and the intensity of
an air stream 17 flowing in a direction substantially orthogonal to
the spray direction of the nozzles 1.
[0075] Generally speaking, a material being easily processable and
having conductivity, such as stainless steel, is preferable as the
material of the spray block 30. If the inside diameter of the spray
port of the nozzle 1 is too small, the spray port may have a risk
of being blocked; conversely, if the inside diameter is too large,
liquid drooping may occur. Hence, the inside diameter is preferably
in the range of 0.1 to 1.0 mm. The through hole serving as the
spray port of the nozzle 1 is processed accurately by drilling.
Furthermore, at the time of press working, the nozzle 1 is formed
to have a height (the distance between the tip serving as the spray
port and the root of the nozzle 1 having a conical shape) of at
least 5 mm to take advantage of the property that charges are
concentrated at pointed portions. The upper portion of the spray
block 30 having the conductive plate 2 and the nozzles 1 formed as
described above is covered with the insulating cover 9 made of an
insulating resin, and the spray block 30 and the insulating cover 9
are fastened to each other.
[0076] The insulating cover 9 serves as a lid for covering the
concave space formed in the conductive plate 2 and having a tray
shape, thereby preventing the solution containing the polymeric
substance injected from the material holding tank 15 via the
material supply pipe 14 into the concave space in the conductive
plate 2 from being contaminated with pollution substances, etc. The
solution stored in the concave space in the conductive plate 2
flows into the nozzles 1 integrally provided at the bottom section
of the conductive plate 2 and is sprayed.
[0077] In the electrostatic spray apparatus according to Embodiment
1, since an organic solvent, such as toluene, is used as a solvent
for dissolving the polymeric substance, etc. to obtain a solution,
it is preferable that the portions making contact with the
solution, such as the insulating cover 9, the material supply pipe
14 and the material holding tank 15, are made of resin materials
having corrosion resistance, such as fluororesin, PE (polyethylene
resin) and PP (polypropylene resin).
[0078] The solution containing the polymeric substance to be
supplied from the material holding tank 15 to the conductive plate
2 via the material supply pipe 14 is uniformly supplied to the
respective nozzle 1 provided on the bottom face of the concave
space in the conductive plate 2. The level of the solution is
detected at all times using a general-purpose level detector so
that all the nozzles 1 are sufficiently filled with the solution,
so that a predetermined level is maintained in the concave space in
the conductive plate 2, and so that the solution is supplied when
it becomes insufficient.
[0079] As shown in FIG. 7, an installation hole 12 in which the
material supply pipe 14 is installed and a concave section that is
fitted with the solution reservoir of the spray block 30 to
hermetically seal the solution reservoir are formed in the
insulating cover 9. The material supply pipe 14 and the spray block
30 are configured so as to be easily removable from the insulating
cover 9, thereby having structures being excellent in
maintainability, such as cleaning.
[0080] The housing constituting the outer face of the spinning unit
22 is made of a resin serving as an insulating material and having
sufficient rigidity to support its own weight and is provided with
a flange 11 so that the housing is installed on the duct of the
collecting section 13. The spinning unit 22 is configured such that
the flange 11 of the housing 10 is screw-fastened to the duct by
bolts to allow easy removal. An opening serving as an air intake
port 6 and being used as means for forming an air stream is formed
on the rear face side of the housing 10, that is, on the side
opposite to the flange 11. A metal net 16 electrically insulated
from the housing 10 is provided at the air intake port 6. The metal
net 16 is connected to a second power supply 50. A voltage that is
lower than that supplied from the above-mentioned first power
supply 40 and is identical therewith in polarity is supplied from
the second power supply 50. The reference potential is the
potential at the wall face of the duct constituting the collecting
section 13, and the reference potential of the first power supply
40 and the second power supply 50 is also the potential at the wall
face of the duct. Furthermore, the reference potential is usually
at the ground potential.
[0081] When a high voltage is applied from the first power supply
40 to the conductive plate 2, charges are generated by an
electrostatic field. Since the charges have the property of being
concentrated at pointed portions, they are concentrated at the tips
of the nozzles 1. The high voltage to be applied to the conductive
plate 2 is determined depending on the material and viscosity of
the solution, the material and diameter of nanofibers to be
fabricated, production environment (temperature and humidity), etc.
and is in the range of several kV to several ten kV. Since the
charges are concentrated at the tips of the nozzles 1 as described
above, the surface tension portions of the liquids at the tips of
the nozzles 1 become a charged state. Hence, minute charged
particles 3 at the tips of the nozzles 1 are separated from the
tips of the nozzles 1 and sprayed as charged liquid droplets by the
strong electric field generated between the nozzles 1 and the first
collector 4 disposed so as to be opposed to the nozzles 1 via the
insulating sheet 5. Since the sprayed charged liquid droplets have
the same polarity, they are repulsed from one another due to the
Coulomb forces exerted therebetween and dispersed uniformly and
then attracted to the first collector 4.
[0082] The distance from the tips of the nozzles 1 to the first
collector 4 is preferably in the range of ten-odd cm to several ten
cm. In Embodiment 1, the distance is set to 20 cm. The distance
from the tips of the nozzles 1 to the first collector 4 is
determined in consideration of the specifications of nanofibers to
be fabricated, the value of the applied voltage, etc. Hence, the
positions of the first collector 4, the insulating sheet 5 and the
nozzles 1 may be made changeable relatively.
[0083] Since the atomized liquid particles sprayed from the tips of
the nozzles 1 are charged as described above and the charges are
attracted to an electrode having the different polarity, the liquid
particles are attracted toward the first collector 4. While the
charges are on the way toward the first collector 4, the liquid
particles are broken up repeatedly many times into minute particles
by electrostatic repulsion because of the charges on the liquid
particles. When the liquid particles are broken up into the minute
particles in this way, the solvent used as a solvent for dissolving
the material to obtain the solution evaporates, and only the
material of nanofibers is left. The material is in the state of
fibers referred to as nanofibers having a diameter of several
nanometers to several ten nanometers.
[0084] Even when the solution containing the polymeric substance is
transformed into the state of nanofibers as described above, that
is, even when the solution is transformed into the solid state, the
charges first given by the nozzles 1 remain preserved, and the
nanofibers remain charged.
[0085] In the spinning unit 22 of the electrostatic spray apparatus
according to Embodiment 1, the insulating sheet 5 is disposed
between the nozzles 1 and the first collector 4 while having a
distance of several mm to the first collector 4. The distance
between the first collector 4 and the insulating sheet 5 is set
within a range from several mm to several ten mm in consideration
of the material of the polymeric substance, the amount of charges,
etc. The insulating sheet 5 is made of a dielectric material and is
formed into a sheet shape or a thin plate shape.
[0086] The insulating sheet 5 has the property of a dielectric
material; in other words, it has the property of inducing electric
polarization by an external electric field, that is, the property
of indicating induced polarization. Hence, when a high voltage is
applied, the surface of the conductive plate 2 serving as a metal
block is charged, and induced polarization occurs. In the induced
polarization, the face of the insulating sheet 5 opposed to the
spray ports of the nozzles 1 has the same polarity as that of the
metal block. Hence, since the material that is sprayed from the
spray ports of the nozzles 1 and is transformed into nanofibers has
the same polarity as that of the insulating sheet 5, the material
is repulsive to the charged insulating sheet 5 by the Coulomb
forces exerted such that "charges of the same polarity repel each
other." As a result, the material transformed into nanofibers is in
the state of floating in the space of ten-odd cm to several ten cm
between the spray ports of the nozzles 1 and the insulating sheet
5.
[0087] The second power supply 50 is connected to the metal net 16
disposed on the rear face of the spinning unit 22 of the
electrostatic spray apparatus according to Embodiment 1, and a
voltage of several ten V to several hundred V is applied to the
metal net 16. The polarity of the voltage applied to the metal net
16 is the same as that of the voltage applied to the nozzles 1. On
the other hand, a voltage of several V is applied to a second
collector 7 disposed inside the collecting section 13 so as to be
opposed to the metal net 16, and the polarity of the voltage is
different from that of the metal net 16. The voltage applied to the
second collector 7 is set within a range of several V to several
hundred V in consideration of the material of the polymeric
substance, the amount of its charges, etc. or set to the ground
potential serving as the reference potential. Therefore, the
charged nanofibers in the state of floating in the space between
the spray ports of the nozzles 1 and the insulating sheet 5 are
repulsive to the metal net 16 having the same polarity as that of
the charged nanofibers and attracted toward the second collector 7
having the different polarity by the Coulomb forces.
[0088] Furthermore, the electrostatic spray apparatus according to
Embodiment 1 is configured such that dry air is passed through the
metal net 16 of the spinning unit 22 installed on the collecting
section 13 and fed toward the second collector 7 inside the duct of
the collecting section 13. The pressure inside the duct of the
collecting section 13 is made lower than the ambient air pressure,
that is, a negative pressure, so that the nanofibers can be
collected securely. Furthermore, the humidity of the dry air fed
into the spinning unit 22 is set to 40% or less so that the
nanofibers floating inside the spinning unit 22 are transferred in
the dry state.
[0089] As described above, the electrostatic spray apparatus
according to Embodiment 1 is configured so as to be able to
securely collect the nanofibers inside the collecting section 13 by
setting the pressure inside the collecting section 13 to a negative
pressure, by setting the polarity of the second collector 7 to the
polarity different from that of the metal net 16 or to the ground
potential, and by feeding dry air from the metal net 16 to the duct
of the collecting section 13. The electrostatic spray apparatus
according to Embodiment 1 is configured such that a fan is provided
for each spinning unit 22 to feed indoor dry air (humidity, 40% or
less). However, the electrostatic spray apparatus may be configured
such that a duct is provided to feed dry air having a desired
humidity from the outside of the apparatus.
[0090] In Embodiment 1, the metal net 16 is used to allow dry air
to be fed from the rear face of the spinning unit 22 so that the
air stream 17 toward the collecting section 13 is generated
securely. Other components having this kind of function may also be
used. For example, it may be possible to use a conductive component
having a structure obtained by drilling multiple through holes in a
metal plate insulated from the housing 10.
[0091] The spinning unit 22 of the electrostatic spray apparatus
according to Embodiment 1 is provided with the air intake port 6
having a metal net structure as air stream forming means. However,
the air intake port 6 according to the present invention may have a
structure other than the metal net structure. For example, the air
intake port 6 may have a structure wherein dry air, the pressure of
which is adjusted, is allowed to be introduced from an air intake
port formed at the end on the rear face side of the spray block 30.
In this case, the metal block in which the air intake port 6 is
formed is connected to the first power supply 40, and the voltage
having the same polarity as that of the nozzles 1 is applied to the
metal block. As a result, the air stream 17 from the air intake
port 6 to the collecting section 13 is generated in the space
between the nozzles 1 and the insulating sheet 5, whereby the
charged nanofibers are attracted from the air intake port 6 to the
second collector 7.
[0092] As described above, the nanofibers floating inside the
spinning unit 22 are fed toward the collecting section 13 and
attracted to and collected and laminated on the surface of the
collecting sheet 8 that is transferred along the second collector
7. As a result, a polymeric web formed of the nanofibers can be
made. Hence, the lower the transfer speed of the collecting sheet
8, the longer the time required for the collecting sheet 8 to pass
through the spinning unit 22, whereby the amount of the nanofibers
to be collected and laminated per unit area increases. As a result,
the polymeric web formed of the nanofibers and serving as a
nonwoven fabric to be produced can be made thicker. In addition,
the more the spinning units 22 to be installed on the collecting
section 13, the thicker the nonwoven fabric. This makes it possible
to control the thickness of the nonwoven fabric of the polymeric
web formed of the nanofibers by changing the number of the spinning
units 22 to be installed and/or by changing the transfer speed of
the collecting sheet 8.
[0093] Since the nanofibers sprayed from the nozzles 1 are
collected and laminated on the collecting sheet 8 that is
transferred along the face of the second collector 7, the charges
on the minute charged particles 3 of the nanofibers are not
accumulated in the space between the spray ports of the nozzles 1
and the insulating sheet 5 made of a dielectric material but
transferred toward the second collector 7 along the air stream 17.
Hence, in the electrostatic spray apparatus according to Embodiment
1, the material is sprayed continuously from the nozzles 1, and it
is thus possible to produce a desired nonwoven fabric.
[0094] Hence, the problem encountered in the above-mentioned
conventional apparatuses, wherein charges are accumulated between
the spray ports and the collector, the accumulated charges are
repulsed, and newly charged material particles cannot be sprayed
from the nozzles, is solved by using the electrostatic spray
apparatus according to Embodiment 1 as described above.
[0095] In the electrostatic spray apparatus according to Embodiment
1, dry air is fed through the air intake port 6 of the spinning
unit 22 installed on the collecting section 13, and the pressure
inside the collecting section 13 is made lower than the ambient air
pressure, that is, a negative pressure, to collect the nanofibers.
The feeding speed of the dry air may be low, approximately several
cm/sec, to the extent that the nanofibers are smoothly collected on
the collecting sheet 8 and the air stream inside the spinning unit
22 is not disturbed. A high air speed of several ten cm/sec or more
is not favorable since the nanofibers in the collected state are
stirred by the pressure of the air and the generation of extra
static electricity.
[0096] The structure of feeding the dry air according to Embodiment
1 is used not only to take measures against the dispersion of the
nanofibers but also to make it possible to collect the organic
solvent contained in the material solution. Since the material, a
polymeric substance, used in Embodiment 1 is used in the state of
solution as described above, an organic solvent or the like is used
as a solvent, and a large amount of the organic solvent is consumed
when the production is carried out. In the conventional
apparatuses, collecting the organic solvent evaporating during the
spraying operation is not considered. Hence, health hazards, fires,
etc. due to the evaporated organic solvent as well as health
hazards to human beings due to the dispersion of the nanofibers
have been serious issues to be concerned about. In the
electrostatic spray apparatus according to Embodiment 1, a recovery
unit 19 is disposed at the top of the collecting section 13 so as
to recover the dry air containing the organic solvent or the like
and passing from the inside of the spinning units 22 through the
collecting section 13. This recovery unit 19 is configured such
that the dry air is exhausted using a fan provided in a recovery
device (not shown) installed outside the electrostatic spray
apparatus.
[0097] The operation of collecting the nanofibers in the
electrostatic spray apparatus according to Embodiment 1 will be
further described below.
[0098] Dry air having a humidity of 40% or less is fed into each
spinning unit 22 via the air intake port 6 using transfer passage
forming means, such as a pipe and a duct, and the pressure inside
the collecting section 13 communicating with the spinning unit 22
is set to a negative pressure using the recovery unit 19. With this
configuration, the organic solvent evaporated inside the spinning
unit 22, etc. is not exhausted to the outside of the apparatus but
fed into the collecting section 13 and recovered using the recovery
unit 19. As described above, the electrostatic spray apparatus
according to Embodiment 1 has a structure capable of securely
recovering the evaporated organic solvent without leaking the
solvent outside the apparatus. An exhaust fan is incorporated
inside the recovery unit 19 according to Embodiment 1 as in the
case of a general-purpose draft chamber. The speed of the air
flowing inside the collecting section 13 toward the recovery unit
19 is within the range of approximately several cm/sec to 10
cm/sec, and the pressure inside the collecting section 13 is set to
a weak negative pressure that is lower than the pressure inside the
spinning unit 22 by approximately 0.02 kPa.
[0099] As described above, the electrostatic spray apparatus
according to Embodiment 1 is configured such that the pressure
inside the recovery unit 19 is set to a negative pressure so that
the pressure inside the collecting section 13 is maintained at a
negative pressure, such that the generated nanofibers are laminated
on the collecting sheet 8 inside the collecting section 13, and
such that the organic solvent evaporated in the spinning unit 22,
etc. is recovered via the duct of the collecting section 13.
[0100] In the electrostatic spray apparatus according to Embodiment
1, the structure in which the dry air is fed from each spinning
unit 22 to the duct of the collecting section 13 is important.
However, the structure should only be made such that the air stream
is stably generated inside the spinning unit 22 mainly from the air
intake port 6 to the collecting sheet 8.
[0101] The electrostatic spray apparatus according to Embodiment 1
is provided with a controller capable of independently driving the
respective spinning unit 22, thereby being configured so as to be
able to select the spinning units 22 required depending on a
product to be produced and to drive only the selected spinning
units 22.
[0102] As described above, the electrostatic spray apparatus
according to the present invention can carry out stable
electrostatic spraying operation using the multiple nozzles and can
mass-produce desired products.
[0103] Furthermore, as described above, the electrostatic spray
apparatus according to the present invention makes it possible to
mass-produce nonwoven fabrics and filters formed of nanofibers of
several nanometers [nm] to several ten nanometers [nm] in diameter.
Hence, the filters produced using the electrostatic spray apparatus
according to the present invention can fulfill the requirements for
the conventional filters as a matter of course and can eliminate
dust and bacteria, such as anthrax, that could not be eliminated
using the conventional filters.
[0104] In addition, the filters produced using the electrostatic
spray apparatus according to the present invention has an excellent
effect not only in view of "elimination" but also in view of
"selection." The fact that particles of several nanometers in
diameter are captured makes it possible to not only eliminate
undesired substances but also take out nanoparticles. For example,
in the case of diamond abrasive grains and the like, if only the
abrasive grains of several ten nanometers [nm] in diameter can be
selected, the conventional grinding accuracy is improved by two or
more orders of magnitude. Furthermore, the filters produced using
the electrostatic spray apparatus according to the present
invention can also be used for drug delivery. As described above,
the electrostatic spray apparatus and the method of electrostatic
spray according to the present invention have excellent features
for "selection" in nano-level.
[0105] Moreover, the products produced using the electrostatic
spray apparatus according to the present invention can also be used
for regenerative medicine for generating "artificial biological
membranes" and the like although the medicine is still in the stage
of research at present. The present invention is thus expected to
be also useful in this kind of special field.
INDUSTRIAL APPLICABILITY
[0106] The electrostatic spray apparatus according to the present
invention carries out electrostatic spray stably using multiple
nozzles, thereby being useful for apparatuses intended for mass
production.
* * * * *